Particle counter having a clog and bubble alarm

ABSTRACT

A fluid containing disbursed particles having a conductivity substantially different than the fluid is pumped through an aperture. A pair of electrodes are mounted so that one electrode is on each side of said aperture and an rf signal is imposed upon the electrodes to develop a voltage across the fluid passing through the aperture. The rf signal is modulated by the conductivity of the fluid instantaneously passing through the aperture so that when a high resistance particle passes through the aperture, the rf signal intensity increases in relationship to the rf signal intensity when fluid is passing through the aperture. The rf signal is then detected, filtered and amplified to provide pulses corresponding to the particles passing through the aperture. Means are provided for counting the pulses and for providing a readout indicating the number of particles contained in a unit volume of the fluid. A clog alarm driver circuit is connected to receive the filtered rf signal and in response to a constant high level filtered signal provides an output to an alarm for indicating a clogged aperture. The amplified signal is directed to an amplifier clipper which further amplifies the signal and establishes a base line at 8 volts DC with pulses having an amplitude of approximately 4 to 6 volts. The presence of bubbles at the aperture causes an erratic signal which appears as base line noise and includes excursions below the 8 volt DC base line output. These excursions intermittently turn on a transistor which provides an output signal to a bubble alarm driver which in response thereto provides an output to the previously-mentioned alarm. A continuous alarm indicates a clogged aperture while an intermittent alarm indicates the formation of bubbles at the aperture.

United States Patent Haynes Oct. 23, 1973 [75] Inventor: John L. Haynes,Redwood City,

Calif.

[73] Assignee: Becton, Dickinson and Company,

East Rutherford, NJ.

[22] Filed: July 14, 1972 [21] Appl. No.: 271,753

[52] U.S. Cl 340/243, 235/92 PC, 324/71 CP [51] Int. Cl. G08b 19/00,G06m ll/OO, GOln 27/00 [58] Field of Search 340/243, 239; 235/92 PC;324/71 CP; 3l7/DIG. 3

[56] References Cited UNITED STATES PATENTS 2,656,508 l0/l953 Coulter3l7/DIG. 3 3,083,909 4/1963 Glaser et al 235/92 PC 3,ll4,257 l2/l963Foster et al 324/71 CP 3,165,692 l/l965 lsreeli et al. 324/71 CP3,603,875 9/l97l Coulter et al 235/92 PC Primary ExaminerJohn W.Caldwell Assistant Examiner-Daniel Myer Attorney-David S. Kane et al.

[57] ABSTRACT A fluid containing disbursed particles having aconaperture and an rf signal is imposed upon the electrodes to develop avoltage across the fluid passing through the aperture. The rf signal ismodulated by the conductivity of the fluid instantaneously passingthrough the aperture so that when a high resistance particle passesthrough the aperture, the rf signal intensity increases in relationshipto the rf signal intensity when fluid is passing through the aperture.The rf signal is then detected, filtered'and amplified to provide pulsescorresponding to the particles passing through the aperture. Means areprovided for'counting the pulses and for providing a readout indicatingthe number of particles contained in a unit volume of the fluid.

A clog alarm driver circuit is connected to receive the filtered rfsignal and in response to a constant high level filtered signal providesan output to an alarm for indicating a clogged aperture. The amplifiedsignal is directed to an amplifier clipper which further amplifies thesignal and establishes a base line at 8 volts DC with pulses having anamplitude of approximately 4 to 6 volts. The presence of bubbles at theaperture causes an erratic signal which appears as base line noise andincludes excursions below the 8 volt DC base line output. Theseexcursions intermittently turn on a transistor which provides an outputsignal to a bubble alarm driver which in response thereto provides anoutput to the previously-mentioned alarm. A continuous alarm indicates aclogged aperture while an intermittent ductivity substantially differentthan the fluid is alarm indicates the formation of bubbles at the pumpedthrough an aperture. A pair of electrodes are aperture mounted so thatone electrode is on each side of said 7 Claims, 3 Drawing Figures 4 4244 4/ 50 MULTI SIGNAL FILTER AMPLIFIER AMPLIFIER VIBRATOR DETECTORSHAPER I CLIPPER 56 ELECTRODE 2 CLOG BUBBLE COUNTING HOUSING ALARM ALARMCIRCUT DRIVER DRIVER ALARM READ OUT PARTICLE COUNTER HAVING A CLOG ANDBUBBLE ALARM BACKGROUND OF THE INVENTION 1. Field of the Invention Thepresent invention relates to particle counters for counting particlessuspended in a fluid medium and more particularly to a counter having analarm for indicating the existence of an aperture clog or the formationof bubbles adjacent the aperture.

2. Description of the Prior Art The prior art in the field of particlecounting may be described by considering the more limited field of bloodcell counting. Pure electronic blood cell counters have been developedwherein changes in conductivity of a diluted blood sample were sensed toprovide an output corresponding to the number of blood cells in thesample. The more sophisticated of these pure electronic blood cellcounters passed a known volume of diluted blood through an aperture anda DC electric signal was applied to electrodes positioned at each sideof the aperture to develop a voltage corresponding to the instantaneousconductivity of the blood sample passing through the aperture. Sinceblood cells have extremely low conductivity as compared to the diluentused to dilute the blood, each time a blood cell passed between theelectrodes, the voltage between the electrodes would increase andprovide a pulse output. The pulses were counted to provide an outputcorresponding to the number of blood cells in the sample.

The problems experienced with aperture-type systems included cloggedapertures resulting from the accumulation of lint and dust in theaperture and the formation of bubbles which appeared as blood cells asthey bounced around the aperture. In order to detect aperture cloggingand bubble formation, the devices of the prior art included anoscilloscope to view a trace of the voltage developed across theaperture so that any abnormality could quickly be detected. Theoscilloscope had to be continuously observed to determine if cloggingwas taking place.

Thus, the devices of the prior art required the use of an oscilloscopeto determine if any abnormalities existed that would adversely effectthe blood cell count provided by the instrument. The inclusion of anoscilloscope in the prior art made their cost prohibitive and restrictedtheir use to major hospitals and large laboratories.

SUMMARY OF THE INVENTION The present invention contemplates a particlecounter that may also be used as a blood cell counter that providespracticing physicians, veterinarians and laboratories with a simple,reliable and accurate instrument for counting white and red blood cells.The instrument automates the tedious task of physically countingindividual blood cells and provides circuitry for automatically warningthe user of such a device when an abnormality is present that mayadversely affect the blood cell count.

The operational concept of the counter is based upon the difference inelectrical conductivity between particles to be counted and the fluid inwhich the particles are suspended. When used as a blood cell counter,the device depends upon the difference in conductivity between bloodcells and the diluent used to prepare blood samples. The diluted bloodsample is drawn through an aperture so that as individual blood cellspass through the aperture, the resistance across the aperture abruptlyincreases. An rf signal is applied to electrodes on each side of theaperture so that the signal is modulated by the variation of theresistance between the electrodes as blood cells pass through theaperture. The modulated rf signal is coupled to a signal detector whereit is demodulated to provide pulses corresponding to the blood cellspassing through the aperture. The rf frequency is greatly attenuated bypassing the signal through a low-pass filter after which the pulses areamplified and shaped and then processed through an amplifier clipperwhich amplifies the pulses and clips the base line at a DC bias level.The pulses are then processed through a counting circuit which includesmeans for accumulating and counting pulses and for providing an outputcorresponding to the number of blood cells per unit volume which isdisplayed on a readout means.

Flow restrictions caused by particulate matter caught in the aperturecause the resistance across the aperture to approach exceedingly highlevels so that the signal output from the low-pass filter approximates aDC signal of substantial amplitude sufficient to trigger a clog alarmdriver which has an output to an alarm for providing a continuousindication which represents a clogged aperture.

When bubbles form about the aperture, they tend to vibrate back andforth, causing the resistance across the aperture to fluctuate up anddown by extremely small amounts. This fluctuation results in an erraticsignal output which appears as base line noise and includes excursionsbelow the 8 volt DC bias level of the amplifier output. These excursionsare used to trigger a transistor that provides an output for driving abubble alarm driver. The bubble alarm driver provides an output to thepreviously-mentioned alarm which provides intermittent indicationscorresponding to the negative excursions previously mentioned. Thus, asingle alarm is used to indicate a clogged aperture when a constantindication is provided and is also used to indicate the presence ofbubbles when intermittent indications are provided.

The main objective of the present invention is to provide a blood cell.counter having an alarm system for I providing indications ofapertureclogging and the presence of bubbles.

Another objective of the present invention is to provide a blood cellcounter that uses a single indicator to indicate either a cloggedaperture or the presence of bubbles adjacent the aperture.

Another objective of the present invention is to provide a blood cellcounter whereina single indicator provides a constant indication whenthe aperture is clogged and an intermittent indication when bubbles arepresent adjacent the aperture.

The foregoing objectives and advantages of the invention will appearmore fully hereinafter from a consideration of the detailed descriptionwhich follows, taken together with the accompanying drawings wherein oneembodiment of the invention is illustrated by way of example. It is tobe expressly understood, however, that the drawings are for illustrativepurposes only and are not to be considered as defining the limits of theinvention.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram illustrating the systemof the present invention.

FIG. 2 is a schematic block diagram showing the electrical system of thepresent invention.

FIG. 3 is an electrical schematic showing the amplifier clipper circuitshown in FIG. 2.

DESCRIPTION OF THE INVENTION The present invention pertains to devicesfor counting particles suspended in a fluid medium, wherein the mediumand the particles have substantially different conductivities. Theinvention will be described as a blood cell counter, but it is to beunderstood that it could be used for counting other types of particlessuch as dust or pollution.

Referring to FIG. 1, there is shown a diagrammatic representation of thesystem of the present invention. An electrode housing 2 receives areservoir bottle 4 containing a diluted blood sample 6. A dip tube 8extends downwardly from the electrode housing into the blood sample 6contained in bottle 4. A cavity 10 is formed in the upper portion of theelectrode housing and is divided into first and second chambers 12 and14 by a partition 16 having an aperture 18 formed therein for connectingthe first and second chambers. Dip tube 8 extends into the first chamber12 of cavity 10 for communicating bottle 4 with chamber 12. Aperture 18has a diameter of 90 microns, a diameter that was chosen because of itsrelationship to the size of a normal red blood cell. Electrodes 20 and22 are mounted in the electrode housing 2 and extend into the first andsecond chambers respectively. The electrode housing and the partition 16are formed of nonconductive material so that the electrodes remainelectrically isolated from each other and do not short out through theelectrode housing.

A sump bottle 24 has a hollow interior which is in communication withthe second chamber 14 through a flexible tube 26. A vacuum pump 28 ispneumatically connected with the interior of sump bottle 24 through aflexible tube 30 for evacuating sump bottle 24 so that the pressurewithin the bottle is maintained below atmospheric pressure and thediluted blood sample 6 from the reservoir bottle 4 is drawn through diptube 8 and into the first and second chambers 12 and 14 so as toestablish a flow of blood sample through aperture 18.

Electronic circuitry 34 impresses an rf signal across the electrodes todevelop a voltage across the electrodes dependent upon the instantaneousconductivity of the diluted blood sample passing through the aperture.

Blood cells have substantially lower conductivity than the diluent usedfor diluting the sample and therefore, abrupt voltage increases orpulses are generated each time a blood cell passes through the aperture.The electronic circuitry 34 senses the pulses and processes them toprovide an output corresponding to the number of blood cells per cubicmillimeter of blood sample passing through the aperture. This output isdisplayed on a readout device 36, such as a meter.

Referring to FIG. 2, there is shown a schematic diagram of the overallelectronic circuitry of the instrument of the invention. A multivibrator38 provides a squarewave output at a frequency of 330 KHZ with a 2O voltpeak output. The output of multivibrator 38 is connected to a signaldetector 40 through a resistor 41. The input of the signal detector isconnected to electrode 22 of the electrode housing 2 while electrode 20is connected to ground.

A voltage divider is formed by resistor 41 and the resistance acrosselectrodes 20 and 22 so that the 330 KHz signal supplied bymultivibrator 38 is modulated as the resistance across the electrodesincreases when a blood cell passes through the aperture. Signal detector40 functions as a demodulator and amplifier to provide a rectifiedsignal to a low-pass filter 42 which eliminates the rf component of thesignal. The low-pass filter is a 6 pole Butterworth Filter which passesfrequencies below 33 KHz; therefore, the output of the lowpass filter isa series of pulses corresponding to blood cells passing through theaperture. The filter output pulses are provided to an amplifier shaper44 for pulse amplification. The output of amplifier shaper 44 isconnected to the input 46 of an amplifier clipper 48 which has an output50 for providing pulses having an amplitude of approximately 4 to 6volts at a bias of 8 volts The output so of amplifier clipper 48 isconnected to a counting circuit 52 which includes a counting means foraccumulating and counting the pulses received from the amplifier clipperand for providing an output signal corresponding to the number of pulsescounted. The output of counting circuit 52 is connected to a readoutdevice 54, such as a meter for providing an indication corresponding tothe number of blood cells per unit volume of blood sample.

A clog alarm driver 56 is connected to the output of the low-pass filter42 and comprises a transistor biased to turn on at a predeterminedvoltage level. The clog alarm driver has an output connected to an alarm58, such as an indicator light which in response to the output providesan indication. When the aperture becomes clogged, the resistance acrossthe aperture increases substantially so that the rf carrier signalincreases in amplitude resulting in a high level DC signal from thelow-pass filter that exceeds the predetermined voltage level at whichthe clog alarm driver turns on. Since a clog is a constant condition,the DC level remains constant and the alarm provides a constantindication.

Amplifier clipper circuit 48 has a second output 62 which is connectedto a bubble alarm driver 60 which in response to an output signal fromthe amplifier clipper provides an output to alarm 58 causing the alarmto provide an indication. The bubble alarm driver is a standard drivercircuit that provides an output in response to an input signal.

Referring to FIG. 3, there is shown a schematic diagram of the amplifierclipper circuit 48 shown in FIG. 2.,Terminal 46 is connected to thenon-inverting input of an operational amplifier 64. Series connectedresistors 66 and 68 are connected between a 28 volt DC source and groundto form a voltage divider for establishing a DC bias level at thejunction between the two resistors. A resistor 70 connects the junctionbetween the resistors 66 and 68 to the non-inverting input of amplifier64. The output of amplifier 64 is connected to terminal 50 of theamplifier clipper circuit and in addition thereto, it is connected tothe inverting input of amplifier 64 by a feedback loop consisting of aresistor 72 and a potentiometer 74 for providing a variable resistancein the feedback loop. A series connected resistor 76 and capacitor 78are connected between the inverting input of amplifier 64 and ground. Atransistor 80 has an emitter connected to the inverting input ofamplifier 64, a base connected to the output of amplifier 64 and acollector connected to output 62 of the amplifier clipper circuit. Aresistor 82 and a capacitor 84 are connected in parallel between thecollector of transistor 80 and ground.

In operation resistors 66 and 68 are adjusted to that an 8 volt DC biasis established at the output of amplifier 64 and potentiometer 74 isadjusted so that the pulses are 4 to 6 volts in amplitude above the 8volt DC base line. In normal operation, transistor 80 remains in a cutoff condition since the base is subjected to a higher voltage than isthe emitter. When bubbles are formed adjacent the aperture, they tend tovibrate about the aperture prior to passing through the aperture. Thevibrating bubbles cause the aperture resistance to fluctuate by anextremely small amount such as 0.1 per cent. This fluctuation appears asbase line noise on output 50 of amplifier clipper 48. The noise includesexcursions below the 8 volt DC base line. The negative excursions causetransistor 80 to turn on thereby clipping the negative going signals.The current through transistor 80 when it turns on is sensed by resistor82 and capacitor 84 and causes capacitor 84 to become charged. If aoscillating bubble is present, a continuous train of negative goingsignals is produced so that capacitor 84 receives a continuous train ofcharges and develops a voltage which appears on terminal 62 of theamplifier clipper circuit and is used to drive the bubble alarm driver60 when a specified threshold voltage is exceeded.

Thus, when bubbles are formed adjacent the aperture, intermittent outputsignals are provided to the bubble alarm driver so that the alarm 58provides an intermittent flashing indication indicative of the presenceof bubbles as distinguished from the constant indication which isindicative of a clogged aperture. The present invention provides aninexpensive circuit for providing alarms that indicate the presence ofbubbles adjacent the aperture or the existence of a clogged aperture andthereby eliminates the necessity for the use of an oscillosclope asrequired by the prior art devices. The circuit makes it possible to usea single alarm indicator for providing indications of both apertureclogging and bubble formation.

What is claimed is:

1. An instrument for counting particles suspended in a fluid medium,wherein the fluid medium and the particles have differentconductivities, comprising:

an aperture;

means for passing the fluid through the aperture;

means for applying an electrical signal across the aperture;

detecting means for detecting changes in the electrical signal levelacross the aperture and for providing an output having pulsescorresponding to the changes in the electrical signal which result froma change in impedance across the aperture as particles pass through theaperture;

means for counting the pulses from the detecting means that exceed apredetermined level and for providing an indication corresponding to thenumber of particles per unit volume of the fluid;

clog detecting means responsive to the output from the detecting meansfor sensing when the detecting means provides a constant outputexceeding a predetermined level resulting from a clogged aperture andfor providing a steady state signal output in response thereto;

bubble detecting means responsive to the output from the detecting meansfor detecting erratic and rapidly changing pulses which result from theformation of bubbles adjacent the aperture and for providing anintermittent signal output in response thereto; and

indicator means, responsive to the signal outputs from the clog andbubble detecting means, for providing a con-stant indication when aclogged aperture exists and for providing an intermittent indicationwhen bubbles are formed adjacent the aperture.

2. An instrument as described in claim 1, wherein the clog detectingmeans comprises a driver circuit biased to provide a signal output whenthe output of the detecting means exceeds a predetermined level.

3. An instrument as described in claim 1, wherein the bubble detectingmeans comprises:

an amplifier clipper circuit for providing an output signalcorresponding to the output of the detecting means but biased at a DClevel; and

means for detecting when the amplifier clipper circuit output signaldrops below the DC bias level as a result of errotic and rapidlychanging pulses and for providing the intermittent signal output inresponse thereto.

4. An instrument as described in claim 3, wherein the amplifier clippercircuit comprises:

an operational amplifier having a first input for receiving the outputfrom the detecting means;

a biasing circuit connected to the first input for establishing a DCbias level; and

a feedback loop connecting the amplifier output to a second input, sothat the amplifier provides anoutput signal biased at a DC level.

5. An instrument as described in claim 4, wherein the means fordetecting when the output signal drops below the DC bias level includesa transistor having the base to emitter junction connected between theoutput and the second input of the operational amplifier so that thetransistor is turned on when the output signal drops below the DC biaslevel.

6. In a particle counting apparatus of the type, wherein a fluid mediumcontaining particles having a conductivity different from the fluid ispassed through an aperture and electrodes positioned at each side of theaperture are energized to develop a signal corresponding to theimpedance across the aperture so that the particles cause signal changesas they pass through the aperture and the changes are detected andcounted to provide a readout corresponding to the number of particlesper unit volume of the fluid medium, the improvement comprising:

clog detecting means for detecting a steady state electrical signalacross the electrodes that exceeds a predetermined level and forproviding a constant output in response thereto;

bubble detecting means for detecting erratic signal changes across theelectrodes and for providing an intermittent output in response thereto;and indicator means connected to the last two mentioned means andresponsive to the outputs therefrom for providing a constant indicationin response to the output of the first mentioned means and anintermittent indication in response to the output of the secondmentioned means so that the constant indication is provided when anaperture clog exists and an intermittent indication is provided whenbubbles are formed adjacent the aperture.

7. An instrument for counting the number of particles per unit volumesuspended in a fluid medium, said fluid medium having a conductivitydifferent than the particles, comprising:

an aperture; 7

means for passing the fluid through the aperture;

means for applying an electronic signal across the aperture;

detecting means for detecting changes in the electronic signal levelacross the aperture and for forming pulses corresponding to the changeswhich result from an increase in impedance across the aperture asparticles pass through the aperture;

means for counting the pulses that exceed a predetermined level and forproviding an indication corresponding to the number of particles perunit volume of the fluid;

a clog alarm driver responsive to the output of the detecting means forproviding a steady state output when the aperture is clogged;

a bubble detector and alarm driver responsive to the pulses from thedetecting means for providing an intermittent output when bubbles areformed adjacent the aperture; and

an alarm indicator connected to the output of the clog alarm driver andbubble detector and alarm driver and responsive to the signals therefromfor providing a constant indication when the aperture is clogged and anintermittent indication when bubbles are formed adjacent the aperture.

1. An instrument for counting particles suspended in a fluid medium,wherein the fluid medium and the particles have differentconductivities, comprising: an aperture; means for passing the fluidthrough the aperture; means for applying an electrical signal across theaperture; detecting means for detecting changes in the electrical signallevel across the aperture and for providing an output having pulsescorresponding to the changes in the electrical signal which result froma change in impedance across the aperture as particles pass through theaperture; means for counting the pulses from the detecting means thatexceed a predetermined level and for providing an indicationcorresponding to the number of particles per unit volume of the fluid;clog detecting means responsive to the output from the detecting meansfor sensing when the detecting means provides a constant outputexceeding a predetermined level resulting from a clogged aperture andfor providing a steady state signal output in response thereto; bubbledetecting means responsive to the output from the detecting means fordetecting erratic and rapidly changing pulses which result from theformation of bubbles adjacent the aperture and for providing anintermittent signal output in response thereto; and indicator means,responsive to the signal outputs from the clog and bubble detectingmeans, for providing a con-stant indication when a clogged apertureexists and for providing an intermittent indication when bubbles areformed adjacent the aperture.
 2. An instrument as described in claim 1,wherein the clog detecting means comprises a driver circuIt biased toprovide a signal output when the output of the detecting means exceeds apredetermined level.
 3. An instrument as described in claim 1, whereinthe bubble detecting means comprises: an amplifier clipper circuit forproviding an output signal corresponding to the output of the detectingmeans but biased at a DC level; and means for detecting when theamplifier clipper circuit output signal drops below the DC bias level asa result of errotic and rapidly changing pulses and for providing theintermittent signal output in response thereto.
 4. An instrument asdescribed in claim 3, wherein the amplifier clipper circuit comprises:an operational amplifier having a first input for receiving the outputfrom the detecting means; a biasing circuit connected to the first inputfor establishing a DC bias level; and a feedback loop connecting theamplifier output to a second input, so that the amplifier provides anoutput signal biased at a DC level.
 5. An instrument as described inclaim 4, wherein the means for detecting when the output signal dropsbelow the DC bias level includes a transistor having the base to emitterjunction connected between the output and the second input of theoperational amplifier so that the transistor is turned on when theoutput signal drops below the DC bias level.
 6. In a particle countingapparatus of the type, wherein a fluid medium containing particleshaving a conductivity different from the fluid is passed through anaperture and electrodes positioned at each side of the aperture areenergized to develop a signal corresponding to the impedance across theaperture so that the particles cause signal changes as they pass throughthe aperture and the changes are detected and counted to provide areadout corresponding to the number of particles per unit volume of thefluid medium, the improvement comprising: clog detecting means fordetecting a steady state electrical signal across the electrodes thatexceeds a predetermined level and for providing a constant output inresponse thereto; bubble detecting means for detecting erratic signalchanges across the electrodes and for providing an intermittent outputin response thereto; and indicator means connected to the last twomentioned means and responsive to the outputs therefrom for providing aconstant indication in response to the output of the first mentionedmeans and an intermittent indication in response to the output of thesecond mentioned means so that the constant indication is provided whenan aperture clog exists and an intermittent indication is provided whenbubbles are formed adjacent the aperture.
 7. An instrument for countingthe number of particles per unit volume suspended in a fluid medium,said fluid medium having a conductivity different than the particles,comprising: an aperture; means for passing the fluid through theaperture; means for applying an electronic signal across the aperture;detecting means for detecting changes in the electronic signal levelacross the aperture and for forming pulses corresponding to the changeswhich result from an increase in impedance across the aperture asparticles pass through the aperture; means for counting the pulses thatexceed a predetermined level and for providing an indicationcorresponding to the number of particles per unit volume of the fluid; aclog alarm driver responsive to the output of the detecting means forproviding a steady state output when the aperture is clogged; a bubbledetector and alarm driver responsive to the pulses from the detectingmeans for providing an intermittent output when bubbles are formedadjacent the aperture; and an alarm indicator connected to the output ofthe clog alarm driver and bubble detector and alarm driver andresponsive to the signals therefrom for providing a constant indicationwhen the aperture is clogged and an intermittent indication when bubblesare formed adjacent tHe aperture.